Radar and passive RF detection systems having one or more rotating antennas are used in airborne, shipboard and ground based installations. The typical electrical interface to an antenna is one or more radio frequency (RF) transmission line(s). In general, this type of system employs a RF rotary coupler to interconnect the rotating antenna to the electronics that remains stationary relative to the rotating antenna. Such rotary couplers are capable of providing radio frequency (RF) energy to and receiving RF energy from, the rotating antenna(s) through one or more separate transmission lines or channels. A typical rotary coupler with separate transmission lines has one coaxial transmission line (RF channel 1) through which no other RF transmission lines pass. The remaining coaxial transmission lines (RF channels 2 and more) are arranged such that each additional transmission line is coaxial with the other transmission lines, and such that each given additional transmission line allows the other transmission lines to pass through the center of the given additional transmission line.
The rotating antenna assembly may also house sensor electronics to support a variety of different applications. The sensor electronics, housed in the rotating antenna assembly, require the bi-directional flow of data and/or control signals and these signals are typically passed through a rotary device which provides the interface to the stationary platform electronics.
Traditionally the data/control signal for sensor electronics, in a rotating antenna application, is realized with a multi-circuit slip ring assembly. Multi-circuit slip ring assemblies are designed to pass electrical data/control signals. Some draw-backs with this technology include the potential for a large number of circuits required to support the electronic bus architecture, potential bandwidth limitations in passing data across a multi-circuit slip ring assembly and potential EMI (electromagnetic interference) concerns in high power RF applications. It is also not uncommon for certain applications, such as airborne installations, to have physical packaging constraints which will limit the available volume for a slip ring installation which could limit system capability.
FIG. 1 is a cross sectional view of a conventional two channel radio frequency (RF) rotary coupler assembly 100 having a stator portion 102 and a mating rotor portion 104. Rotary coupler 100 is configured to transmit two RF channels, referred to as Channel 1 and Channel 2, across rotational interface/s of the coupler 100 that are formed between mating stator portion 102 and rotor portion 104 of the coupler 100. Channel 1 is a RF channel transmitted on the central axis of rotary coupler 100 and Channel 2 is a RF channel transmitted off of the central axis of rotary coupler 100. As shown, a stationary coaxial signal input 113 is provided on stator portion 102 for the RF signals of Channel 1, and a stationary coaxial signal input 115 is provided on stator portion 102 for the RF signals of Channel 2. Similarly, a rotating (rotor) coaxial signal output 114 is provided on rotor portion 104 for the RF signals of Channel 1, and a rotating (rotor) coaxial signal output 116 is provided on rotor portion 104 for the RF signals of Channel 2.
Still referring to FIG. 1, rotor portion 104 is rotationally guided relative to stator portion 102 by a pair of ball-bearing assemblies 144. Rotary coupler 100 is sealed to allow for control of the internal environment which is exposed to RF energy by, o-ring seals 145 between parts of the coupler that do not rotate relative to each other, and by wiper seals 146 provided between parts of the rotor 104 that rotate relative to parts of the stator 102 of the rotary coupler 100. RF energy is conducted through Channel 1 of rotary coupler 100 by way of a transmission line formed between the surfaces of the internal cavities 147a and 147b. RF energy is conducted through Channel 2 of rotary coupler 100 by way of a transmission line with matching stub circuits formed between the surfaces of internal cavities 148a and 148b. Between the rotor portion 104 and stator portion 102 of the rotary coupler 100, RF energy of Channels 1 and/or 2 is made to pass by close-fitting concentric cylindrical surfaces separated by a thin layer of dielectric material which form corresponding stepped impedance chokes 117, 118, 119 and 120, between the rotor and stator portions 104 and 102 of the rotary coupler 100.
As shown in FIG. 1, a coaxial transmission line is provided for transmitting RF signals of Channel 1 between stationary coaxial signal input 113 and rotating coaxial output 114, and a coaxial transmission line is provided for transmitting RF signals of Channel 2 between stationary coaxial signal input 115 and rotating coaxial output 116. Specifically, a center conductor is provided for Channel 1 that includes a stationary on-axis inner conductor portion 122 in RF signal communication with a rotating on-axis inner conductor portion 121 across a rotational interface formed by close-fitting concentric cylindrical surfaces of an innermost stepped impedance choke 117 that is located between the stationary portion 122 of the inner conductor of Channel 1 and the adjacent rotating portion 121 of the inner conductor of Channel 1. An outer conductor is formed for Channel 1 by stepped impedance choke 118 that is located between the stationary portion 192 of the outer conductor of Channel 1 and the adjacent rotation portion 191 of the outer conductor of Channel 1. Similarly, a center conductor is provided for Channel 2 that includes a stationary off-axis inner conductor portion 192 in RF signal communication with a rotating coaxial inner conductor portion 191 across a rotational interface formed by close-fitting concentric cylindrical surfaces of a stepped impedance choke 120 that is located between the stationary portion 192 of the inner conductor of Channel 2 and the adjacent rotating portion 191 of the inner conductor of Channel 2. Similarly, an outer conductor is formed for Channel 2 by outermost stepped impedance choke 119 that is located between the rotating portion 181 of the outer conductor of Channel 2 and adjacent stationary portion 182 of the outer conductor of Channel 2 and the bearing inner race support housing 125.
FIG. 2 is a partial enlarged view 200 of the stepped impedance choke 117 of the rotary coupler assembly 100 of FIG. 1. As shown, the stepped impedance choke 117 is formed between stationary on-axis inner conductor portion 122 of the Channel 1 transmission line and the rotating on-axis inner conductor portion 121 of the Channel 1 transmission line. Also shown, the stepped impedance choke 118 is formed between stationary outer conductor portion 192 of the Channel 1 transmission line and the rotating outer conductor portion 191 of Channel 1 transmission line.